February 16, 2011

Questioning the gap between anatomical and behavioral modernity

A central tenet of the consensus view on modern human origins is that anatomical modernity (first attested in the Omo skulls from Ethiopia, ~195ky) precedes behavioral modernity (clear signs of symbolic thinking, such as painting, decoration, burial, etc.) by about 150 thousand years. The latter is said to be most clearly attested in "Cro-Magnon"-type people from Europe, although precedents of this type are occasionally detected in older archaeological cultures.

Yet fossil morphology combined with studies of DNA both from fossils and from living humans now shows that Neanderthals and their associated archaeological record are largely irrelevant for models concerning early phases of H. sapiens evolution (Harvati, Frost, and McNulty 2004; Serre and Paabo 2006).

I would say that the recent 2010 articles on Neandertal/Denisovan intermixture with modern humans makes the notion of Neandertal irrelevance problematic. Indeed, while the author of the current paper argues for behavioral variability in anatomically sapiens populations predating the "Upper Paleolithic Revolution", I would say that an equally important aspect of variability is that related to non-sapiens populations such as Neandertals. That is, we should question not only the exclusion of chronologically older sapiens populations from behavioral modernity, but also contemporaneous non-sapiens ones.

Shea is dismissive of the Neandertal intermixture hypothesis, stating that:

Whatever one thinks about this issue, it is simply a fact that during the period under discussion, 50–200 kya, H. sapiens was an African primate.

I am not sosure about that. We have evidence for ~100ky anatomically modern humans in China, Arabia, the Levant (Qafzeh), and North Africa. A quite recent genetic study discounts the recent Out of Africa paradigm, opting instead for either a Multiple Archaic populations model, or an ancestral bottleneck 150 thousand years ago in Africa.

A significant part of the paper's argument is focused on the occurrence of different lithic technologies across time and space in Africa. The argument, as far as I can understand it, is that Mode 5 microlithic technologies of the European Upper Paleolithic type do not represent an innovation worthy of an idea of "progress" or particular newly-hatched cognitive skills:

Microlithic technologies occur in African contexts sporadically between 50 and 100 kya (Ambrose 2002). They become common and widespread after 20 kya, not just in Africa but also in Eurasia (Elston and Kuhn 2002). However, one ought not read too much into this difference. Small retouched stone tools are known from many Eurasian Lower and Middle Paleolithic contexts (Dibble and McPherron 2006; Zaidner, Ronen, and Burdukiewicz 2003). Small geometric-backed pieces are known from Last Interglacial (presumably Neanderthal) contexts in Germany (Conard 1990). Whatever cognitive capacities mode 5 microlithic technologies require were plainly ones that were either evolutionarily primitive or evolved convergently in the genus Homo.

While Shea questions the behavioral non-modernity of early East Africans such as Omo, Schwartz and Tattersall question the label of "archaic Homo sapiens", suggesting that recent Homo sapiens (of the period of the "Upper Paleolithic Revolution" and recent humanity) can be anatomically defined in a manner excluding of these earlier hominins. Another recent study gives me no great confidence that Rhodesian Man (Kabwe) commonly identified as ancestral to the Omo "archaic sapiens" deserves that position.

So, should we extend the definition of sapiens in both its anatomical and behavioral aspects to 200ky East Africans, or should we limit it (per S&T's suggestion) in both senses to humankind of the last few tens of thousands years?

My personal preference, stated several times in this blog, is to think in terms of a recent demographically dominant "Afrasian" population that absorbed other archaic humans in Africa ("Paleo-Africans") and Eurasia (Neandertals/Denisovans/?).

Recent genetic evidence (every time we sampled an "archaic" hominin we found that it can't be fit to a pure Out of Africa model) suggests to me that intermixture between deeply divergent human populations was the norm, rather than the exception, and assimilation models, or even multiregional evolution may be true, the latter.

As for the onset of "behavioral modernity" I envision two scenaria:

An accretion of genetic changes across interbreeding hominins across the globe led to a demographic explosion, which led to more beneficial mutations in the ever-larger human population, which led to an even more successful human population (in both the behavioral and demographic senses)

A cognitive leap allowed a portion of Homo (the Afrasians) to multiply, expand, and dominate over all other hominins, absorbing them in the process.

Whether one questions the concept of behavioral modernity or not, I think it's undeniable that something happened ~50ky ago leading to the extinction (via assimilation or competition) of so many not-modern looking populations across Eurasia.

Current AnthropologyVol. 52, No. 1 (February 2011), pp. 1-35

Homo sapiens Is as Homo sapiens Was

John J. Shea

Abstract

Paleolithic archaeologists conceptualize the uniqueness of Homo sapiens in terms of “behavioral modernity,” a quality often conflated with behavioral variability. The former is qualitative, essentialist, and a historical artifact of the European origins of Paleolithic research. The latter is a quantitative, statistically variable property of all human behavior, not just that of Ice Age Europeans. As an analytical construct, behavioral modernity is deeply flawed at all epistemological levels. This paper outlines the shortcomings of behavioral modernity and instead proposes a research agenda focused on the strategic sources of human behavioral variability. Using data from later Middle Pleistocene archaeological sites in East Africa, this paper tests and falsifies the core assumption of the behavioral-modernity concept—the belief that there were significant differences in behavioral variability between the oldest H. sapiens and populations younger than 50 kya. It concludes that behavioral modernity and allied concepts have no further value to human origins research. Research focused on the strategic underpinnings of human behavioral variability will move Paleolithic archaeology closer to a more productive integration with other behavioral sciences.

19 comments:

I feel like Einstein must have felt 1904 or so, with all the strange evidence in plain sight out there, but pieces not-quite-yet (but almost) falling into place. Exiting times - I have no doubt that in five to ten years, people will slap their foreheads (that they didn't come up with ****).

Having said that, stone tools are obviously not a good measure of cultural nor intellectual achievement. But with the conventional indicators (burials, ocher, body adornments, extreme food variety, exchange distance of trade items, musical instruments, visual art) we simply have a rather limited set of data points.

"Having said that, stone tools are obviously not a good measure of cultural nor intellectual achievement. But with the conventional indicators (burials, ocher, body adornments, extreme food variety, exchange distance of trade items, musical instruments, visual art) we simply have a rather limited set of data points."

Comparative ethnology, comparative musicology and comparative linguistics should be included into the studies of the origins of "behavioral modernity" much more consistently. This “vertical” integration of cultural data across the past and the present is no less important than the “horizontal” integration of cultural data across fossil hominid species.

If we look at culture holistically across archaeology and ethnology/linguistics/musicology, we'll see two poles of cultural "expression": the Euro-African one characterized by a wealth of Upper Paleolithic and Late Stone Age artifacts from 40K on but low levels of linguistic and cultural diversity (only 20 language stocks in Africa, much fewer types of mythological motifs, more standardized social organization across vast geographic distances, etc.) and the Asian-Amerindian-Australasian one characterized by the paucity of the former (in America only 15K) and the extreme diversification of the latter (140 language stocks in America; very rich forms of social organization and folkloric motifs). This uneven distribution probably reflects differences in long-term population size. More densely populated areas are prone to more innovation and diffusion, while more sparsely populated areas are more prone to descent with modification.

A sapient behavioral revolution (or the sapient behavioral paradox, as Renfrew calls it) is supported by a myriad of uncontroversial facts such as the unprecedented level of technological sophistication, impact on the environment, the disappearance of previous hominid species, the proliferation of languages and cultures all over the globe across all ecological habitats, etc. All of these indications of behavioral revolution(s) are worldwide. Archaeologically, the first stable indications of a new type of behavior that has resulted in all these changes are only 40K years old. This is remarkable.

On a separate note, independent innovation seems to be a powerful driver of technological change. Pressure flaking must have emerged at least 3 times in 3 different places in the Pleistocene (Blombos Cave at 75K in Africa, Soluteran at 22K in Europe and Clovis at 12K in America). Some “mental structures”/”cultural codes” invisible in the archaeological record may have got activated to produce three very similar outward technological expressions.

50,000 years ago Homo sapien populations reached a density that allowed for the free flow of ideas between groups. Mental connections were made by people and new ideas exploded on the scene. Culture develops at a much faster pace than DNA.

You may not, but I do. Although it's admittedly somewhat speculative, and I have yet to write it up formally, at least so far as the relationship to technological behavior. (But see here.)

My idea is that an improvement in language skills enabled the use of epic (e.g. the Iliad), which permitted descriptions of technology to be transmitted across long distances in space and time, such as the description of the tower shield which is thought to have been 6 centuries obsolete when Homer wrote.

We find occasional inventions of the same sort of technology seen after ~50KYA long before that time, but it soon vanishes. After that time, there's a much stronger tendency for technology to remain in use. Improved communications across both space and time would be a plausible (IMO likely) explanation.

CF the discussion in Guns, Germs, and Steel by Jared Diamond regarding the retention and loss of technology (e.g. the boomerang in New Zealand).

"As for the onset of 'behavioral modernity' I envision two scenaria:An accretion of genetic changes across interbreeding hominins across the globe led to a demographic explosion, which led to more beneficial mutations in the ever-larger human population, which led to an even more successful human population (in both the behavioral and demographic senses)A cognitive leap allowed a portion of Homo (the Afrasians) to multiply, expand, and dominate over all other hominins, absorbing them in the process".

"Euro-African one characterized by a wealth of Upper Paleolithic and Late Stone Age artifacts from 40K on but low levels of linguistic and cultural diversity."

I agree with much of what you wrote, but the above statement relates to present times, after several linguistic, agricultural, and standing armies sweeps, and cannot possibly be traced back 40,000 years. What can you possibly know about the linguistic diversity 40,000 - 10,000 ya? The Caucasus is a good region to re-consider linguistic and genetic diversity (or the lack thereof) in Europe.

charles,

"50,000 years ago Homo sapien populations reached a density that allowed for the free flow of ideas between groups. Mental connections were made by people and new ideas exploded on the scene. Culture develops at a much faster pace than DNA."

When climate suddenly improves (like it did 50,000 ya) and food is plenty and easily available / reached by low-energy hunting, a population may easily double in just one generation. Using a generation time of 20 years, this means a ~1,000-fold explosion in just 200 years, and a ~1,000,000 times explosion in as little as 2,000 years. In other words, huge human populations should have been the norm at any time climate was favorable. But only 50,000 years ago it made a difference, while at the same time it did not increase Neanderthal population size significantly (just a slight eastward expansion).

AK"My idea is that an improvement in language skills enabled the use of epic"

I commented on something similar on Maju's blog. Language skills, and the ability to communicate in a common language at far distances (rather than just a few neighboring groups away), is obviously a very important element. But how did this arrive within a few thousand years almost simultaneously across the (old) world? Didn't a paper highlighted a couple of days ago make a point that genetic sweeps are extremely rare, in humans?

The ability to look beyond upbringing and prejudice even just a few tens of km away, and to embrace other cultures and languages, and the motivation to accept them and to learn a new language and to contribute to a (paleolithic) regional lingua franca seems to me something primarily cultural - but of course based on a fairly high level skill set.

What did we learn about human behavior from archaeology that we couldn't learn by observing modern human populations? That humans bury their dead, eat their enemies, make stone tools and drink wine out of skull caps? No need to dig around for this. Archaeology has access only to what was left behind in garbage pits. Data from modern human populations deals with what has been passed on through millennia.

"The Caucasus is a good region to re-consider linguistic and genetic diversity (or the lack thereof) in Europe."

Dienekes:Whether one questions the concept of behavioral modernity or not, I think it's undeniable that something happened ~50ky ago leading to the extinction (via assimilation or competition) of so many not-modern looking populations across Eurasia.

Eurologist:Isn't it incredibly frustrating that we have no idea what that was?

I feel like Einstein must have felt 1904 or so, with all the strange evidence in plain sight out there, but pieces not-quite-yet (but almost) falling into place. Exiting times - I have no doubt that in five to ten years, people will slap their foreheads (that they didn't come up with ****).

AK:My idea is that an improvement in language skills enabled the use of epic (e.g. the Iliad), which permitted descriptions of technology to be transmitted across long distances in space and time

I think Dienekes is correct that something dramatic happened, I think Eurologist is correct that we probably have the data right in front of us, but are just not piecing it together, I think Ak is correct that it involves language...

Drumroll please...

I think I'm correct - as I've pointed out here before and on GNXP previously - that the missing link was discovered a year or so ago, when they completed a genome scan of 4 Bushmen (plus Desmond Tutu), and later while examining that data, John Hawkes found a FOXP2 Bushman Variant - here are his words:... one of the five individuals (TK1) has an amino-acid-coding mutation in FOXP2.Yeah, that surprised me when I found it.

I think that it right there - staring at us!!!!!

The point is that most modern humans might carry a novel variant of FOXP2, that Introgressed 42,000 years ago from another human lineage - like Neanderthals for example - that led to a rapid selective sweep. So, what we're seeing in Bushmen is not a recent mutation, but the ancestral state of FOXP2 in early modern humans.

"50,000 years ago Homo sapien populations reached a density that allowed for the free flow of ideas between groups. Mental connections were made by people and new ideas exploded on the scene. Culture develops at a much faster pace than DNA." --- The climate may have been right in the past for the expansion of Homo sapiens but there are many factors that determine an outcome. For example when the climate changed and populations shrunk, so did the flow of ideas. This has not happend in the last 50,000 years. We have had a long run of cultural transmission. Possibly this was curtailed in the past. There had to be a combination of events that had never occured before. I would think that this would be an admixture with pre-existing Homo poulations that introduced certain new genes that gave us a cognitive advantage not seen before. Creativty seems to play a large role our cultural explosion. The passing on of ideas through story telling and pictures and fugurines is important. Admixture, the symbolic representation of ideas, and population density to keep the ideas alive is the key to the 50, 000 year explosion.

"In other words, huge human populations should have been the norm at any time climate was favorable. But only 50,000 years ago it made a difference"

"surely we have every reason to accept that population numbers have fluctuated greatly over the period of our existence, whether we include Australopithecus or not. I'd be fairly certain that the fluctuating level of hominid remains is more than a little the result of fluctuating hominid population numbers. Whenever conditions are right populations of any species eventually reach the maximum carrying capacity of the environment. The so-called 'balance of nature' is very flexible.

"at the same time it did not increase Neanderthal population size significantly (just a slight eastward expansion)".

Wasn't that expansion eastwards a little earlier than that? About 70,000 years ago?

pconroy: "The point is that most modern humans might carry a novel variant of FOXP2, that Introgressed 42,000 years ago from another human lineage - like Neanderthals for example - that led to a rapid selective sweep. So, what we're seeing in Bushmen is not a recent mutation, but the ancestral state of FOXP2 in early modern humans."

Does it mean that Bushmen are less fluent in their language than Neanderthals were in their(s)? There's nothing in Bushmen languages that betrays an earlier stage in the evolution of human language. Their clicks - unique among human languages - are superimposed on a typical phonological inventory. This is consistent with some of them carrying a derived state of FOXP2.

I agree with Hawks who pointed out that a selective sweep 42,000 years ago is way too recent for a variant with a global distribution. What I think is happening is that certain lineages shared between human and Neaderthals have a slower mutation rate than some African-specific lineages.

I have lately been posting about Bushmen on Razib as well http://blogs.discovermagazine.com/gnxp/2011/02/real-three-dimensional-pca/

"The point is that most modern humans might carry a novel variant of FOXP2, that Introgressed 42,000 years ago from another human lineage - like Neanderthals for example - that led to a rapid selective sweep".

And:

"There had to be a combination of events that had never occured before. I would think that this would be an admixture with pre-existing Homo poulations that introduced certain new genes that gave us a cognitive advantage not seen before".

Both situations are basically a product of hybrid vigour, a very likely scenario if all the pre-modern human populations contained limited numbers. Hybrid vigour through crossing of different regional species of plants has certainly several times led to the hybrid plant becoming classified as a noxious weed.

"How did this arrive within a few thousand years almost simultaneously across the (old) world? Didn't a paper highlighted a couple of days ago make a point that genetic sweeps are extremely rare, in humans?"

The process I'm looking at involves a more widespread organization in which small groups are tied together by traveling bards (or whatever you want to call them). Judging by the evidence of Homer, the epic tradition (by which I mean the entire set of stories and formulas by which they were communicated in epic, see Oral Tradition in Wiki) contained a massive number of formulas in various dialects, some current (we think) at the time Homer is supposed to have written, some archaic or completely obsolete, ranging back (IIRC) to before the time of the dialects attested in Mycenaean.

Such a tradition could tie together a large number of small communities with different dialects, covering a much larger area than for a single dialect. IMO intelligibility is a function partly of attitude: somebody listening for similarities in a different speech paradigm (dialect) could find it intelligible while somebody with a rejective attitude would consider it babble.

The presence of an epic tradition, with all these different dialects represented, would "pre-adapt" (in a nurturative sense) members of any local speech paradigm to try much harder to communicate with people speaking another.

Between this, and the existence of stories about distant regions (shared between bards), there would be far greater incentive for small bands of young adult explorers (probably mostly male) to travel long distances, thus contributing to increased genetic homogenization, as well as keeping cultures much more in touch technologically.

I envision a slowly expanding population containing substantial proportions of people with some or all of the necessary genetic improvement(s), probably involving alleles of a number of genes on different chromosomes. As this population got larger, the overall rate of technological invention would increase (due to more inventors and opportunities for invention), which in turn would produce more effective competitors (especially with other cultures).

At some point this population (probably speaking a single language group with a single epic tradition) would reach "critical mass" and begin to expand as fast as it could increase population, wiping out and/or absorbing (most of) the inferior humans in its path.

I'd expect that any local group that fell away from the epic tradition would quickly become non-competitive due to the loss of access to new technology, as well as the absence of kin links to other groups. (Intermarriage would probably be through capture/rape without maintenance of kin obligations with the results.)

Obviously (IMO) any local group with reduced capacity for use of epic would be far more likely to drop out of the greater interaction group (maintained through the epic tradition), and die out. The result would be a rapid expansion of the original population with some minor admixture from replaced populations, with a great deal of homogenization spreading what contributions were accepted throughout the expanding group.

IIRC there's evidence that the "Cro Magnon" retained full genetic mixture until sometime like 18-25KYA, after which more northern populations began to show adaptations to extreme cold such as shorter limbs.

Obviously, this is a very light brush over the subject, and formally writing it up will require many hours of searching out references and explaining technical issues from many different fields, which I don't have time for right now. But at least it gives the flavor.

"The point is that most modern humans might carry a novel variant of FOXP2, that Introgressed 42,000 years ago from another human lineage - like Neanderthals for example - that led to a rapid selective sweep. So, what we're seeing in Bushmen is not a recent mutation, but the ancestral state of FOXP2 in early modern humans."

It's not implausible I guess, but IMO your suggestion involves a mis-use of parsimony. Changes to genes such as FOXP2 tend to produce massive homeotic mutation (hopeful monsters), when they have any effect at all. I'm really envisioning a much larger suite of new alleles of different genes, with some variation in effect: some people are capable of composing formulas on the fly (during performance), some people are barely able to understand unusual word orders in inflected/agglutinative languages (without memorizing the formula) and thus cannot really understand the epic performances their fellows are enjoying, and most people would fall somewhere in-between.

Of course, the mutations producing the differences between human and chimpanzee/gorilla might also have produced "hopeful monsters", although the capacity for new phosphorylation might have required some additional changes to make effective use of it. I'm inclined to date these mutations to before the beginning of language (as better than what bonobos can achieve), while only the last step would have taken place 40-50KYA.

Eurologist: "What can you possibly know about the linguistic diversity 40,000 - 10,000 ya? The Caucasus is a good region to re-consider linguistic and genetic diversity (or the lack thereof) in Europe."

I'll pick up this point again. If you read Johanna Nichols's "Linguistic Diversity in Space and Time" (1992), you'll see her approach to making sense of linguistic diversity in the Pleistocene. She compared grammatical elements across vast distances and came up with two macroregions based on the recurrence of interconnected grammatical elements: Asia/Australasia/America and Europe/Africa. The first macroregion she considers a refugial zone, the second a spread zone. A refugial zone results from population accretion and is characterized by high levels of linguistic diversity. A spread zone results from several population spreads and is characterized by linguistic homogeneity. The Caucasus is a refugial zone in the middle of a massive spread zone. It maintains grammatical similarities with Australasia/America (such as "active" grammar in Kartvelian which has close matches in North America) but has little in common with Africa. The Eurasian/Africa spread zone of course experienced massive population spreads in the Neolithic but these spreads began even earlier, with the arrival of modern humans into these areas from East Asia in the Pleistocene.

My point, though, is that it is very hard to quantify European linguistic diversity 40,000 to 10,000 years ago. Yes, I agree there were probably at most two meaningful migrations into Europe before LGM, and probably not more than 4 meaningful refuges, but 4 refuges plus perhaps 2 post-LGM migrations from the East before the advent of agriculture makes for much more diversity than we see today, even including outliers like Basque and Finno-Ugrian.

"Yes, I agree there were probably at most two meaningful migrations into Europe before LGM, and probably not more than 4 meaningful refuges, but 4 refuges plus perhaps 2 post-LGM migrations from the East before the advent of agriculture makes for much more diversity than we see today, even including outliers like Basque and Finno-Ugrian."

And I'm not denying that linguistic diversity in Europe (and Africa) has been reduced over the past 40,000 years. But as we go deeper into the past, our comparative sample becomes more and more global and, as European Pleistocene diversity deteriorates with the influx of more numerous Holocene populations, more recent (including some current) extra-European populations become likely proxies for the lost diversity within Europe. Comparative method doesn't recognize unattested data, especially if this unattested data is being agnostically called out as holding a crucial key to the past. CM works with attested data as either direct or indirect evidence for past variation.

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